It comes after a protest called for the governing body to let Aerts race.

At the Koppenbergcross in Oudenaarde on Tuesday (November 1), a group unveiled banners saying "Let Toon start so he can go to the hairdresser already" and "UCI wake up".

Aerts is not cutting his hair in the hope a hair sample could help his defence against a positive test for a metabolite of letrozole, a banned substance usually used to treat breast cancer.

The positive test came from a sample taken on January 19 and Aerts has consistently maintained his innocence. 

Aerts competed at the UCI Cyclo-cross World Championships later that month, finishing sixth in the men's race, before being notified of an adverse analytical finding (AAF) on February 14.

The UCI has clarified that letrozole does not carry a mandatory provisional suspension and that it has not suspended Aerts, so if he is not racing that is through choice.

"Letrozole and its metabolites are qualified as Specified Substances on the World Anti-Doping Agency's Prohibited List," said the UCI in a statement. 

"In such cases there is no mandatory provisional suspension required and Mr Aerts was not provisionally suspended by the UCI. 

"Any rider may, however, decide to accept a provisional suspension and refrain from participating in competitions on a voluntary basis.

"In accordance with the UCI Anti-Doping Regulations, the UCI afforded Mr Aerts the opportunity to provide his explanations for the AAF.

"Mr Aerts elected to do so, and during that process he made several requests which he deemed necessary to support his explanations. 

"The UCI respected Mr Aerts' procedural rights at all times, and assisted him with all relevant enquiries with third parties."

If Aerts competes and is later given a suspension for an anti-doping violation, the ban would begin from the day after his last competition.

Aerts needs to prove letrozole came to be in his system through no fault of the athlete to avoid punishment, or admit to an AAF.

If the rider refuses to admit to the charges, the case will be taken to the UCI Anti-Doping Tribunal. 

The Belgian has claimed the substance could possibly have been in a recovery shake.

Letrozole is an aromatase inhibitor and lowers estrogen levels.

Italian tennis player Sara Errani is among other athletes to have tested positive for letrozole.

Errani - who claimed to have ingested the substance through a family meal prepared by her mother, who was taking letrozole - was banned for 10 months.

Aerts has twice won the overall UCI Cyclo-cross World Cup title, is a three-time bronze medallist at the World Championships and is a former European champion.